The development of drugs aimed at reducing obesity and controlling eating disorders represents a major target of the pharmaceutical industry and has become one of the most exciting areas in drug discovery. The long term goal of this project is to develop tools for high throughput testing of drug compounds from combinatorial libraries that target G-Protein-Coupled Receptors (GPCR's) associated with appetite control and eating behavior. Novel targets for such drug development arise from the recent explosion of information on molecules and neural circuits involved in appetite regulation. This proposal focuses on developing testing platforms for GPCR families associated with feeding behavior. A distinguishing feature of the drug-discovery strategy we are pursuing is that is based on an efficient and highly reliable system that allows multiplexing of receptors in order to test numerous compounds against numerous targets. This strategy has been enabled by a novel transfection technology that is licensed by Originus, Inc. from the University of Michigan termed Surface Transfection and Expression Protocol (STEP), which has significant advantages over transient and even stable expression methods. Under Phase I funding, testing platforms for two GPCR families associated with feeding behavior-the Melanocortin Receptors (MCRs) and the Orexin Receptors (OXRs) were developed. STEP transfection of 384-we 11 microplates to test the expression and ligand activation of individually expressed MCRs and OXRs (Specific Aim 1) and multiplexing via co-expression of multiple MCRs (Specific Aim 2) were validated in two different cell lines. Under Phase II funding, we propose to build on the information from Phase I to validate platforms for other feeding-related GPCRs with different intracellular coupling, to extend the testing to additional cell lines, to develop new assays for HTS, to optimize allelic variants of the GPCRs, and to multiplex GPCRs of the same or different families in physiological relevant combinations. Finally we propose to initiate our own internal efforts for HTS of multiplexed GPCRs with single ligands per microplate well from a small library of known compounds and for ultraHTS (uHTS) of multiplexed GPCRs using pools of drugs from larger chemical libraries in each microplate well. The proposed experiments have been carefully designed based on interactions with many potential business partners and will allow Originus to demonstrate the efficacy of the STEP platforms for screening multiplexed feeding-related GPCRs and other GPCRs outside the immediate area of obesity drug screening. The proposed Phase II work will be the basis for the implementation of more broadly HTS and uHTS of libraries and testing of potential lead compound in collaboration with selected partners during Phase III.